bundle - Parceling objects in android to transfer from one activity to another -

recently interviewer asked me tricky question. there several parts of question.

1. why (question why , not how) need parcel objects while sending 1 activity , not send directly

answer gave -

parcelable gives capability developers restrict object creation in way makes faster use.

i confused on part, decided site difference between using serializable , parcelable :p (clever huuuhhh !), http://www.developerphil.com/parcelable-vs-serializable/ used reference.

2. while using bundle, when use string, int not need parcel data, think string/int default internally parcelled ?

answer gave -

because string/int primitive data-type, if had used wrapper class directly, might possible had use parcelable(i not sure on part)

i did not useful link after googling, or interviewer not quite satisfied answer. if guys can help, wonderful !

why (question why , not how) need parcel objects while sending 1 activity , not send directly

parcelling/serializing objects isn't speed had guessed.

when you're sending data between activities, , between different applications (remember intent objects aren't meant communication between own activities, between yours , of other apps well), cannot expect sender , receiver have access same memory address spaces.

android's documentation states applications run in own discrete memory spaces. here's quote effect docs:

each process has own virtual machine (vm), app's code runs in isolation other apps.

so when want send object myobject receiving activity, can't send reference/pointer because receiver won't have access location specified pointer. instead you'll have send representation of myobject receiver can access , use -- why need marshall data form can unmarshalled, , easiest way have class of object implement serializable lets java best convert object array of bytes can sent , unmarshalled receiver. since serializable uses reflection, slow.

you can use other ways faster marshall data -- one, example, converting object json representation using library gson , sending across since json document can represented string , converted java object. way, faster in pretty cases using parcelable interface lets specify exactly how want marshall data , exactly how should unmarshalled. gives more control on transmission of object.

the tl:dr: parcelling/serializing etc used because can't send memory addresses across, have send actual data of object , has represented in form.

while using bundle, when use string, int not need parcel data, think string/int default internally parcelled ?

how bundle works internally puts map , parcels/unparcels data needed (ie when get/put called). putting objects bundle, object's class needs implement serializable or parcelable because needs tell bundle how should marshalled/unmarshalled internally.

but primitive types , strings simple enough , used enough developer doesn't need specify how needs happen , bundle provides convenience methods it. can't give solid answer @ lowest level of how works because lot of parcel code natively implemented , couldn't find online, must straightforward convert representation in bytes.